Uni-directional high level low frequency sound source



Oct. 31, 1961 L. R. PADBERG, JR 3,007,133

UNI-DIRECTIONAL HIGH LEVEL LOW FREQUENCY SOUND SOURCE Filed Jan. 12. 1956 2 Sheets-Sheet 1 IN VEN TOR.

LOU/3 R. PADBERG Oct. 31, 1961 1.. R. PADBERG, JR

UNI-DIRECTIONAL HIGH LEVEL LOW FREQUENCY SOUND SOURCE Filed Jan. 12, 1956 2 Sheets-Sheet 2 HIGH VOLTAGE SOURCE INVENTOR. LOU/.5 R. PADBERG ATTORNEYS United States atent 3,007,133 UNI-DIRECTIONAL HIGH LEVEL LOW FREQUENCY SOUND SOURCE Louis R. Padberg, Jr., 4126 Middlesex Drive, San Diego, Calif.

Filed Jan. 12, 1956, Ser. No. 558,812 12 Claims. (Cl. 340-12.)

(Granted under Title 35, U.S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to unidirectional high level low frequency sound sources and more particularly to means in underwater applications for generating a high intensity sound having a steep wave front whereby the signal is sharp and intense, such as that generated by an explosive.

One such instrument for producing explosion induced shock waves is known as a cone ring. A dynamite cap and a length of primacord is detonated along the axis of the ring which, because of its mechanical configuration gives a series of shock waves which forms a wave train lasting for a very short period of time. Thus a frequency results which'is dependent upon the time duration of the wave and the number of rings in the device. While this device produces the desired energy level, much of the energy is lost in unwanted directions, it takes time to repeat the process and there is always danger in the handling of explosives. In devices using an electrical spark across a gap between electrodes, these electrodes are housed in a container of fresh or distilled water or other fluid of high resistance. The fluid and electrodes form a capacitor charged by a current. The spark results from the condenser-breakdown effect between the two electrodes, producing energy which is exerted against a diaphrain in the chamber. Transmitting through an intervening diaphram results in less efiiciency. The spark resulting from the condenser-breakdown effect is accomplished with relatively small capacitors and a very high voltage. Since high potentials are always more dangerous, particularly in Water, safety precautions must be observed.

The device comprising the present invention consists of a shock ring assembly and an arrangement of spark gaps placed along the axis of a large cone reflector. The surrounding fluid such as sea water is used to initially make electrical contact between the electrodes. This shoi causes current to flow momentarily, heating the water in the gap between the electrodes. The temperature at the gap becomes very high momentarily, causing the water to be vaporized. A gas bubble is formed which expands and collapses resulting in the generation of a shock wave at the beginning and end of the bubble. The duration of this pulse is extremely short. In this invention a line of spark gaps is arranged along the axis of a cone made up of ring reflectors. As the shock waves pass through'these rings additional shock waves are set up and the net result is a train of shock waves. The direction of propagation is mainly out the apex of the cone. In order to gain additional directivity so that the arrangement is uni-directional, the ring assembly is placed along the axis of a larger cone reflector. The outer reflector is backed with an acoustic material which prevents the sound from passing through. The desired low frequency can be derived by a proper selection of the number of rings, by varying the spacing of the rings, and by controlling the duration of the pulse train. By using lower potentials with very large capacitors in generating the spark, the equipment is safer to handle.

An object of the present invention is to provide a high "ice intensity low frequency sound source for use in seismic exploration and underwater applications.

Another object is the provision of a sound source for generating sound having a steep wave front, whereby the signal is sharp and intense, such as that generated by explosives.

Another object is the provision of apparatus for converting a single shock wave into a wave train having definite frequency characteristics.

Another object is the provision of apparatus for generating explosive sounds under water by means other than the use of explosives whereby the sounds may be repeated at will without raising the apparatus from the water to prepare it for the next operation.

Still another object is to provide a high intensity sound source that has uni-directional characteristics.

A further object is the provision of a high intensity sound source for generating sounds of a desired frequency.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of the device Without the core reflector; and

FIG. 2 is a schematic view showing the relationship of arts.

p When an electric field exists between two electrodes in a gaseous atmosphere, the free electrons in the field accelerate toward the anode. If the field strength exceeds a certain critical value, this electron movement initiates several phenomena which involve the formation of electron avalanches and ion clouds and the production of photons (energy in the form of light) in a complex process which ultimately results in a completely ionized, low-resistance path through which the discharge occurs. The discharge in water is more complex. When extremely high potentials are applied across an electrode gap immersed in an electrically conducting fluid such as sea water, the ensuing electrical discharge thereacross causes sudden and rather large increases in temperatureof the order of thousands of degrees Fahrenhei'tin said fluid between the electrodes. As a result, if that fluid is water, for example, it becomes vaporized and a gaseous bubble is formed. This bubble then expands and collapses, whereupon another bubble forms and collapses, with this process of bubble forming, expanding, and collapsing alternately occurring as long as the electrical potential is applied to the electrodes at a critical level. The alternate bubble expansion and collapse causes the radiation and propagation of acoustic waves comprising sharp pressure pulses.

The frequency of this acoustic or sonic energy wave radiation is dependent upon a number of factors, most of which may be varied within the design limits of this invention without violating the scope or spirit thereof. For instance, such variable factors could include spacing of the electrodes, size of the electrodes, materials of the electrodes, amount of electrical energy employed, and the submersion depth of the subject sound source in the aqueous or other fluid medium within which it is operating. However, for most practical purposes, the maximum spectral energy occurs at a frequency which is approximately the reciprocal of the bubble pulse interval.

The phenomena associated with the bubble formation, expansion, and contraction are ostensibly of considerable complexity; however, experimental operation of the subair. O'f course, the expansion and collapse of the electric arc formed bubbles may be readily observed during the operation of the device of the present invention in accordance with the principles thereof. Each time the gas bubble expands and collapses a sharp pressure wave is sent out. It is the aim of this invention to send out a train of these very high pressure waves instead of just a single pressure pulse.

The shape and size of the electrodes has a considerable bearing upon the operation of the sparkgap. Since the energy dissipated during the breakdown is directly proportional to the capacitance discharged it should be desirable to have as high a gap capacitance as possible. But the higher the capacitance the lower the source impedance must be to charge it to the breakdown voltage in a specific time interval (T=resistance capacitance). If it is desired to interrupt the discharge at very-fast rates, then the capacitance must be small or the condenser will nottake on its full charge. This rate of dischargecauses one to select a large or small condenser, for the particular job at hand. For example, in very shallow seismic work, a sniall ca pacitor would be used. For deep work one would use very large capacitors. Since it takes the sound longer to travel the distance, such rapid discharge rates are not necessary.

Referring now to the drawings wherein like numerals designate like parts in all views, the cone ring assembly 11 comprises a plurality of axially spaced concentric rings 12 of triangular cross-section. 7 As shown the hypotenuse of the right triangle faces the apex of the conical con= figuration. This surface .13 reflectsnoise bursts from a line of spark gaps 14, mo'unted along the axis of the ring assembly, rearwardly to the inner surface of a large cone reflector 16 backed by unicellular rubber. In stead of a single shock wave being emitted, the ring assembly 11 causes a train of shock waves to be reflected through the apex of the cone. The ring assembly is so positioned that the resulting reflections are made to fall in phase with the original shock wave. The end result is a uni-directional train of shockwaves of a desired frequency determined by the number and spacing of the rings '12 and the duration of the wave controlled by a vacuum switch 17. I

Spark plugs with non-corrosive plated multiple dis charge points have been found to be suitable for form ing the spark gaps 14. There are several ways of niount ing and discharging them. A single gap may be mounted near the apex of the cone ring and the explosive energy confined to a point source. The gaps of several spark plugs, or similar devices,- can be connected in series or parallel arrangements and fired singly or in unison Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is: 4 v

1. A uni-directional high level low frequency sound source adapted to project acoustical energy through an electrically conductive aqueous fluid while being submerged therein comprising in combination a plurality of reflecting rings, said reflecting rings each having successively increasing diameters and centers disposed along a longitudinal axis of revolution for defining a conical configuration, reflector means spacially disposed from the outer diameter of said conical reflecting ring configuration having an inner surface substantially parallel theretoand means disposed on said longitudinal axis of revolution for generating electric spark within the confines of said conical configuration.

2. A submarine acoustical sound projector consisting of a plurality of rings having respective diametrical centers spacially disposed along an axis of revolution for defining a predetermined geometrical configuration, means including a pair of electrodes for generating an electric spark on said axis of revolution, and means connected to said plurality of rings and saidspark generating means for supporting same in a fixed relationship.

3. 'Asound source adapted to convert electrical energy into high level low frequency acoustical energy and by means of suitable commutating device's. As illustrated in FIG. 2, the electrodes of the spark gaps 14 are connectable in parallel across the condenser, one electrode of each gap being connectable to the condenser by; way of switch 17 and the other electrode' of eachgap being connected to ground at the other side of the condenser. Thus, when the gaps 14 are immersed in sea water and the switch 17 is closed, the water between the electrodes provides a low impedance discharge path for the condenser, the electrodes being elfeetively shorted by the water path therebetween. In the use of spark plugs, the tops must be Well insulated so that only the points are shorted in the water or much of the energy will be lost.

While it has been found in the use of this invention that a 6 kv. source and a /2' microfarad to 120 microfarad capacitor have been satisfactory, it should be uh derstood that these are not to be considered as limitations and that other values may be preferred under certain conditions.

broadcast same in a redetermined direction througnjafi electrically conductive aqueous fluid while being sub} merged therein comprising in combination a plurality, of 7 energy reflecting rings, said energy reflecting rings each having diflerent diameters and centers disposed along a longitudinal axis of revolution ford'efining a conical configuration having a focal axis coincident with said of revolution, means disposed on said focal axis for generating an electrics'park thereat, and means connectedto said plurality of energy reflectingrings and said spark' generating means for supporting same in substantially fixed relationship.

4. In a sound source adapted to convert electrical energy into high power lowfrequency acoustical energy and transmit same in a predetermined direction through an electrically conductive aqueous fluid while being submerged therein, a plurality of energy reflecting rings each of which has a diametn'cal center disposed along an axis of revolution for defining a predetermined geometrical configuration, said reflector rings having right isosceles triangular cross-sections with one of the two equal sides thereof perpendicular to said axis of revolution,.means for generating an electric spark at said axis of revolution, and means connected to said plurality of energy reflecting rings and said spark generating means for supporting same in a predetermined relationship.

5. In a low frequency submarine sonic shock wave source, a pluralityof wave energy reflecting means each of which is spacially disposed from the others and has a diametrical center positioned along an axis of revolution for defining a predetermined geometrical configura tion, a plurality of electrode means positioned on said axis of revolution adapted to produce an intense electric arc thereacross whenenergized by a high voltage potential, electricallyconductive aqueous fluid means contacting said electrodes for timely shorting same, and means 7 COHDGCtBdutO said electrode means for timely'supplying said high voltage potential thereto and thereby generating said intense electric are within said electrically conductive aqueous fluid means and producing 'and propagating a high power sonic shock wave for subsequent contact with the aforesaid wave energy reflecting means, whereby said sonic shock wave is converted into a train of sonic shock waves having a frequency proportional to said spacial distance therebetween and the geometrical configuration thereof.

6. A sound source adapted to convert electrical energy into high power low frequency acoustical energy and propagate same as a series of sonic shock waves in a predetermined direction through an electrically conductive aqueous fluid while being submerged therein comprising in combination a plurality of sonic energy reflecting rings having diametrical planes the centers of which are respectively spacially disposed along a longitudinal axis of revolution for defining a predetermined geometrical configuration, reflector means spatially disposed from the external portion of said sonic energy refleeting ring geometrical configuration, electrical means adapted to be energized by a high voltage located on said longitudinal axis of revolution for generating a high intensity sonic shock wave within that portion of said electrically conductive aqueous fluid ambient thereto, and means connected to said electrical means for timely supplying said high voltage thereto, whereby said sonic shock wave is successively reflected and projected by the aforesaid sonic energy reflecting rings and said reflector means as a series of sonic shock waves having a directivity and frequency in accordance with the aforesaid geometrical configuration.

7. A uni-directional high level loW frequency sound source adapted to convert electrical energy into acoustical energy proportional thereto and broadcast same within an electrically conductive aqueous fluid comprising in combination a plurality of energy reflecting rings having successively increasing diameters and the centers thereof respectively disposed at equal distances along a predetermined longitudinal axis, said rings each having a right isosceles triangular cross-section with one of the two equal sides thereof perpendicular to said longitudinal axis, a plurality of pairs of electrodes located along said longitudinal axis, conical reflector means spatially disposed from said energy reflecting rings having an axis of revolution coinciding with said predetermined longitudinal axis, means connected to each of said pairs of electrodes for timely generating an electric spark thereacross, and a mounting means connected to said plurality of electrodes and said plurality of energy reflecting rings for supporting same in a fixed relationship.

8. A sound source adapted to convert electrical energy into high level low frequency acoustical energy and project same in a predetermined direction through an electrically conductive aqueous fluid while being submerged therein consisting of a plurality of reflecting rings having successively increasing diameters respectively disposed at predetermined distances along a longitudinal axis, said reflector rings each having right isosceles triangular cross-sections with the bisectors of the right angles thereof respectively intersecting said longitudinal axis at a common junction, a plurality of pairs of electrodes located along said longitudinal axis with each pair thereof having a gap therebetween respectively, conical reflector means spatially disposed from the outside diameter of said reflecting rings having an axis of revolution coinciding with said longitudinal axis, unicellular rubber backing means mounted on the outer surface of said conical reflector means, means for storing and discharging high potential electrical energy, a high voltage source, resistance means interconnecting said electrical energy storing and discharging means and said high voltage source, switch means connected to said electrical energy storing and discharging means, said resistance means, and said plurality of pairs of electrodes for timely discharging said stored electrical energy thereacross and thereby heating and vaporizing that portion of the aforementioned electrically conductive aqueous fluid disposed within said electrode gaps, and forming a rapidly expanding and contracting bubble, whereby a predetermined series of high intensity low frequency sonic shock waves are generated and projected through said electrically conductive aqueous fluid in the aforesaid direction.

9. The device of claim 8 wherein said means for storing and discharging high potential electrical energy includes a capacitor.

16. A projector adapted to convert high potential electrical energy into high level low frequency acoustical energy and broadcast same in a predetermined direction through an electrically conductive aqueous fluid While being submerged therein comprising in combination a plurality of energy reflecting rings having successively increasing diametrical planes spatially disposed from each other along a longitudinal axis at a distance that is proportional to the frequency of the acoustical energy to be broadcast, a conical reflector means equidistantly disposed from the outside diameters of said plurality of reflector rings for receiving reflected acoustical energy therefrom and reflecting said received acoustical energy back therethrough, a like plurality of spark plugs having gaps respectively disposed along said longitudinal axis within said diametrical planes, means connected to said plurality of spark plugs for timely producing a high intensity electric spark across said gaps and thereby vaporizing that portion of the aforementioned electrically conductive aqueous fluid therebetween, whereby a high intensity sonic shock wave is generated thereat and propagated to said reflector rings for reflection therefrom to the inner surface of said conical reflector means for rereflection thereby through said reflector rings in the aforesaid predetermined direction.

11. The device of claim 10 wherein said means connected to said spark plugs for timely producing a high intensity electric spark across said gaps includes a high voltage source, a capacitor adapted to be parallel connected to said plurality of spark plugs for electrical discharge thereto, a resistor connected between said high voltage source and one terminal of said capacitor, and switch means coupled between the interconnection of said high voltage source and said capacitor and the aforesaid plurality of spark plugs.

12. The device of claim 10 wherein said conical reflector further includes a unicellular rubber backing means attached thereto on the side opposite said plurality of reflector rings.

References Cited in the file of this patent UNITED STATES PATENTS 1,152,697 Bodde Sept. 7, 1915 1,731,624 Henry Oct. 15, 1929 1,836,397 Rieber Dec. 15, 1931 1,985,251 Hayes Dec. 25, 1934 2,064,911 Hayes Dec. 22, 1936 2,511,689 Beechlyn June 13, 1950 2,559,227 Rieber July 3, 1951 2,617,874 Lewis Nov. 11, 1952 2,646,852 Forrester July 28, 1953 FOREIGN PATENTS 112,995 Australia Mar. 11, 1948 

